GLUCOSE-TURNOVER IN PRESENCE OF CHANGING GLUCOSE-CONCENTRATIONS - ERROR ANALYSIS FOR GLUCOSE DISAPPEARANCE

The present studies were undertaken to determine whether 1) the cold- and hot-GINF techniques used with Steele's model provide equivalent es timates of the rates of glucose appearance (R(a)) and disappearance (R (d)) in the presence of physiological changes in glucose and insulin c oncentrations, 2) the conditions for the best estimation of R(a) are t he same as those for R(d), 3) the magnitude of error (if present) diff ers in diabetic and nondiabetic subjects, and 4) situations exist in w hich the knowledge of R(d) allows inferences to be made on whole body glucose uptake. To do so we performed experiments in non-insulin-depen dent diabetes mellitus and nondiabetic subjects using simultaneous inf usions of [6-H-3]glucose and [6-C-14]glucose; glucose and insulin were infused to mimic normal postprandial glucose and insulin profiles; th e infused glucose contained [6-C-14]glucose but not [6-H-3]glucose. Co mpared with the hot-GINF method, the traditional cold-GINF method unde restimated (P < 0.05) R(a) and R(d) by 10-15% and hepatic glucose rele ase by 25-50% during the 1st h of the study, with the magnitude of err or being the same in both diabetic and nondiabetic subjects. Error ana lysis demonstrated that errors in R(a) and R(d) have different analyti c expressions containing common structural but different volume errors . Both R(a) and R(d) can be accurately measured in diabetic and nondia betic subjects if glucose specific activity is kept constant and the v olume of the accessible pool is used to calculate glucose disappearanc e. The relationship between R(d) and whole body glucose uptake was als o derived. Although R(d) can be determined by relying on measurements in the accessible pool only, the assessment of whole body glucose upta ke requires a model of the nonaccessible portion of the glucose system . However, knowledge of R(d) can provide useful insights into the beha vior of whole body glucose uptake.